For supplying electronic components within a motor vehicle, a generator such as an alternator, is generally used in combination with a vehicle battery. The generator, or alternator is driven by a running motor as a secondary unit. The drive may be effected, for example, by means of a belt drive or directly via a crankshaft. With a driven alternator, a current is provided by the same, for example for charging the vehicle battery and for loads connected to an on-board network. The alternator transforms mechanical energy provided by the motor into electric energy, the mechanical power necessary being approximately proportional to the electrical power output. A non-regulated voltage provided by an alternator strongly varies with the rate of rotation of the motor and the load connected. Since an alternator should be able to build up the nominal voltage of the motor vehicle on-board network already at a low motor speed, it is generally oversized. To keep it from exceeding, as a consequence, an admissible final charging voltage of the vehicle battery in the event of a high rate of rotation, the voltage is generally limited to a maximum value by a regulator.
With three-phase current alternators, the electrically generated excitation field of the driven alternator rotor is influenced by an electronic charging regulator. The regulator generally measures a rectified actual voltage at the output of the generator using a regulator-internal stable reference voltage compares the measured voltage with a setpoint voltage value, and adjusts the strength of the excitation field by means of a higher or lower level of generator field current, flowing through the rotor such that the actual voltage of the generator remains at least approximately constant, independently of load and speed. Conventionally, the generator output voltage is regulated and the generator field current may be limited by the regulator.